Tobacco and alcohol misuse are serious problems in the U.S. and are more prevalent among members of the U.S. Armed Forces. Both conditions account for higher mortality, greater morbidity, higher health care costs, and lost productivity while in the service and afterwards in civilian life. Little information exists from prospective research on predictors of the adoption of these habits while in military service. Such information would prove valuable for the development of interventions and policies for preventing tobacco use and alcohol misuse among military personnel. This application therefore proposes to conduct a comprehensive prospective assessment of military service features and exposures, demographic characteristics, and psychosocial risk factors for tobacco use and alcohol misuse in the Millennium Cohort Study, a 21-year longitudinal investigation of over 150,000 military personnel. This study began enrollment of members of the U.S. Armed Forces in 2001. Follow-up of subjects for both exposures and outcomes is accomplished through administration of a triennial survey and review of Department of Defense electronic personnel and health care databases as well as other national databases. The overall objective of this proposed research will be to identify the effects of exposures during military service on the incidence, persistence and relapse of tobacco use (including smokeless) and alcohol misuse. This objective will be accomplished by prospectively studying these outcomes in relation to exposures experienced at study entry and during military service, such as deployment with and without combat exposure, other military exposures, mental health conditions, military service characteristics and lifestyle factors. In addition, the Family Millennium Cohort Study will begin in 2010 when the spouses of 10,000 study participants will be recruited. This cross-sectional comparison will permit the study of the same predictors of interest as in the prospective study and allow for the first time the assessment of whether military experiences in the service member are associated with tobacco use and alcohol misuse among spouses.